British slang, possibly even specifically London slang. Used to describe
a participant in the peculiarly 90s phenomenon of young women acting in
a similar way to young men when socialising: ie drinking, being raucous
and letching at members of the opposite sex. A female version of the
New Lad in other words, obviously derived from one who is both a geezer
and a bird. Most women I know who this has been applied to take it as a
compliment.